The invention relates to a method of producing a friction lining, whereby a friction paper is displaced with a latex based on an elastomer and fibers of the friction paper are then bonded to one another due to precipitation of the elastomer out of the latex, a friction lining, in particular a friction lining for wet operation, comprising at least one friction paper with fibers which are bonded to at least one elastomer, as well as a friction unit, in particular a motorcycle clutch, comprising a friction lining on a support and a counter plate which co-operates with the friction lining.
For specific use in the friction metals industry, such as motorcycle clutches or in applications using counter plates made from light metal or light metal alloys which are susceptible to wear, it is standard practice to use friction linings with a higher degree of elasticity than the friction linings used for other applications. The reason for this resides in the wear-sensitive counter plate because it is made from light metal or light metal alloys associated with a corresponding reduction in weight as required by the automotive industry. By reducing the weight of the clutch directly, it is possible to achieve an increase in power, especially in the case of smaller engines.
These days, latexes in powdered format are predominantly used to produce such friction paper with a higher elasticity. However, the problem with this is that they are disposed loosely between the fibers of the friction paper as spacers and an adequate bonding is not produced between the individual elements.
Problems also occur when it comes to producing friction linings with high latex contents economically, for example on a paper machine, because when using higher quantities of latex, it can no longer be kept stable and a specifically controlled precipitation of the latex on the fiber surface or in the fiber matrix no longer takes place. In the event of uncontrolled precipitation of the latex, it no longer interacts with the components of the friction paper but tends by preference towards the surfaces of the paper machine. In other words, after only a short production time, large quantities of latex deposits are left on vat walls, stirrers and in pipes. These problems occur with effect from a latex content above 20%. Production becomes impossible due to filling and clogging pipes. The paper machine clogs regularly and becomes uncontrollable. Occasionally, these latex deposits then detach and precipitate in the paper causing faulty areas and irregularities.
So far, attempts to solve this problem by using dispersing agents have failed because it has not been possible to improve the tendency of the latex to deposit or has not been so to a sufficient degree. Since these dispersing agents have a base of surface active agent and are therefore active at the boundary surface, they reduce the surface tension of aqueous solutions, thereby creating an additional and not inconsiderable foam problem.
Friction linings bonded with and containing latex are already described in the prior art. For example, JP 2000-213578 A describes a clutch for wet operation, comprising an annular core element made from a steel plate or an aluminum alloy, which is lined with a friction material on both sides. This wet friction material is produced by impregnating a paper base material with a heat-curable resin. The paper base material is made from normal paper with fibers of an organic or inorganic nature, a filler and latex. The latex content in the paper base material in this instance is in the range of between 0.4% by weight and 25% by weight.
JP 60-139933 A describes a friction element for brakes or clutches of an automotive vehicle or a motorcycle. The friction element is made from paper which contains between 1 and 30% by weight of rubber latex. An NBR or SBR latex is used by preference. This imparts a corresponding elasticity to the friction element and the coefficient of friction of thin paper can be improved. This also reduces resistance to abrasion.